1. Field
Aspects of embodiments of the present invention relate to solid oxide fuel cells (SOFCs).
2. Description of Related Art
A fuel cell is a cell that converts chemical energy generated by oxidation into electric energy. Fuel cells are an eco-friendly technology that generate electric energy from materials such as oxygen and hydrogen, which are abundant on the Earth.
In fuel cells, an electrochemical reaction is performed as an inverse reaction of the electrolysis of water by respectively supplying oxygen and fuel gas to a cathode and an anode, respectively, thereby producing electricity, heat, and water. Therefore, fuel cells produce electricity at high efficiency while causing minimal pollution.
A process of producing electricity using fuel cells will be briefly described. Hydrogen is supplied to the anode, and the supplied hydrogen is decomposed into hydrogen ions and electrons. Then, the hydrogen ions are moved to the cathode through an electrolytic membrane, and the electrons are moved to the cathode through an external electrical wire, thereby generating electric power.
In fuel cells, a majority of the material discharged in the electricity generating process is only water. Hence, there is little to no concern about pollution, and energy generation efficiency is improved by about 40% or more when compared with existing electricity generation technologies. Since certain mechanically moving parts are not required, which are required in general heat engines, fuel cells have various advantages, such as miniaturization, less noise, etc.
Fuel cells are classified into alkaline fuel cells (AFCs), phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), polymer electrolyte membrane fuel cells (PEMFCs), and solid oxide fuel cells (SOFCs), as determined according to a kind of electrolyte used.
Among these types of fuel cells, SOFCs are widely used because the position of an electrolyte is easily controlled, there is no concern about the exhaustion of fuel, and the lifetime (lifespan) of a material (and therefore, the SOFC) is long.
SOFCs are generally classified as tube-types or plate-types according to a shape of a unit cell. In the case of general tube-type SOFCs, a material used as a current collecting wire has low electrical conductivity, but has a high increase in resistance under a high-temperature atmosphere (e.g., high temperature conditions). Therefore, the inherent properties of the material cause the current collecting efficiency to be substantially lowered, due to an increase in resistance and a decrease in conductivity of the current collecting wire in the process of collecting current. Moreover, when the entire volume, e.g., length, of each unit cell is enlarged to increase the electricity generation capacity of the SOFC, the current collecting wire is necessarily lengthened. Accordingly, the total resistance of the current collecting wire is also increased, and a voltage drop is increased at the same time. Therefore, degradation of performance results from voltage loss.